A new one to me just happened. With the app dropping trips, I had to log in to the website which was showing trips intact, but I had lost the waitlist upgrade designation. It reappeared today, but when I looked at the return booking online, the first leg doesn't come up. It is intact on the app, but not sure which version I trust AC to be registering. No hint of time or equipment change and my DW and DD are intact on their parallel booking.
I'll give it a couple more days before I start to panic - we leave in 3 days, and I don't want to be burning vacation time and roaming fees on hold.